1. Field of the Invention
This invention relates to a fuel injection control system for an engine, and more particularly to a fuel injection control system that is suitable for an outboard motor.
2. Description of Related Art
In order to improve engine performance, and in particular fuel efficiency and emissions, many types of engines use a fuel injection system for supplying fuel to the engine. A fuel injection system often includes fuel injectors that directly inject fuel into an air induction device. The amount of fuel injected through the fuel injectors is determined by a control system, which usually includes an electronic control unit (ECU). Typically, the ECU determines the desired amount of fuel and the corresponding fuel/air ratio based upon signal inputs from sensors that detect various engine conditions. The control system can therefore improve performance by precisely controlling the fuel/air ratio for each cycle of the engine and over a wide variety of engine running conditions. The control system can also optimize other engine systems such as, for example, ignition.
Because the ECU typically receives signal inputs from various sensors around the engine, if one of the sensors malfunctions, the ECU may use signal input from other sensors to determine the amount of fuel and the corresponding fuel/air ratio. In such cases, the engine will continue to run; however, the engine would be capable of better performance if data from the failed sensor was available. Operators of watercraft, however, often do not appreciate the reduced performance of the outboard motor or the increase in hydrocarbon and nitrogen oxides emissions. If the operator remains unaware of the sensor malfunction, this condition will remain until the next time the engine is serviced (assuming that sensor diagnostics are performed at the time of service).